The average temperatures of locations throughout the world vary significantly. In addition, extreme temperatures, from peak high to peak low, also vary dramatically throughout the world. For example, recorded temperatures on Earth range from 56.7° C. (134° F.) in Death Valley, California to −89.2° C. (−128.6° F.) in Vostok Station, Antarctica. The extreme temperatures of a single location may also represent a wide temperature range. For example, many locations throughout the world experience high temperatures in summer and cold temperatures in winter.
Despite Earth's varying climates and extreme temperature differences, animals, birds, and even humans inhabit almost every corner of the planet. This proliferation of habitat is astonishing when considering that many animals and birds, and all humans, must maintain thermal homeostasis, and constantly regulate their body temperatures to within only a few degrees Celsius.
The average normal human body temperature varies between about 36.12° C. and 37.5° C. (96.8-99.5° F.). If a person's body temperature rises only 1° C. to 38° C. (100.4° F.), that person may begin to sweat and feel very uncomfortable. At an increase of 3° C. to 40° C. (104° F.), fainting, dehydration, weakness, vomiting, headache, dizziness, and profuse sweating may occur. An increase of 6° C. from normal to 43° C. (109.4° F.), normally results in death.
Likewise, the human body does not fair well in extreme cold. At a decrease of 1° C. to 36° C. (96.8° F.), a person may start to shiver. At a decrease of 3° C. to 34° C. (93.2° F.), severe shivering, loss of movement of the fingers, blueness and confusion may set in. At a decrease of 9° C. to 28° C. (82.4° F.), severe heart rhythm disturbances are likely and breathing may stop at any time.
While temperature ranges for other homeothermal animals may vary from those of humans, an animal's need to thermally regulate its body temperature is similar.
When temperatures are extreme, maintaining a constant body temperature can be difficult even for grown healthy adults. Sleeping outside in cold conditions, such as on a camping trip, may require large sleeping bags or heaters. Playing winter sports may require layers of thermal protection such as gloves, hats and coats. Army soldiers operating in the field under extreme conditions often experience hypothermia or heat exhaustion.
Numerous unsuccessful attempts have been made to address problems associated with regulating body temperature. For example, electric blankets that incorporate resistive heating elements in order to produce extra heat are well known. However, numerous problems exist with typical electric blanket designs. For example, electric blankets require electricity which is often not available during emergencies or in rural areas. Electric blankets also do not distribute heat evenly and may require sophisticated electronics to regulate heat, if regulated at all. Furthermore, the resistive heating elements that are typically woven into the electric blanket may create a fire hazard. In addition, the heating system in electric blankets may be delicate because the small gauge wires that are often used to increase resistance and comfort are susceptible to breaking.
Other devices exist to regulate body temperature. However, a major problem in any of these devices is the complexity of the components that actually control the temperature. U.S. Pat. No. 4,856,294 to Scaringe et al. discloses a device designed to keep the body cool through the use of heat exchange materials that are effectively endothermic in a temperature range that is below normal body temperature. Scaringe discloses a micro-climate cooling vest that uses a heat transfer material that changes phase from solid to liquid within the practical range of 60°-90° F. to cool the body of workers in high temperature environments. The vest is filled with the heat transfer material through fill ports. The entire vest is then placed in an environment capable of freezing the heat transfer material. Once sufficiently cooled, the vest is worn.
While Scaringe discloses the use of an endothermic heat transfer material to cool the body, the design of the micro-climate vest still leaves many problems unsolved. For example, the vest leaves large portions of the body unprotected from the environment including the legs and head which typically generate a majority of body heat and which may need cooling. In addition, vests may be difficult to put on infants or small animals and may not attain the desirable snug fit on their small bodies. Also, it is unlikely that a person in the wilderness or in other extreme conditions such as a soldier in battle would have the necessary heat transfer material to fill the vest. Even if the vest were pre-filled with the heat exchange material, the freezer necessary to prepare the vest for use would likely not exist in environments such as the wilderness, a battlefield, or in the rural areas of developing countries. Furthermore, placing the entire vest in a freezer environment to prepare the vest for use may cool other portions of the vest disproportionately from the heat exchange material, making those portions of the vest much colder than desired.
In the human body, as well as in the bodies of animals, the nervous regulating mechanism regulates body temperature by controlling the body's reaction to temperature. For example, the nervous regulating mechanism may cause goose bumps to form in response to cold, or may cause the body to sweat in response to heat.
While temperature regulation may be difficult even for healthy adults, infants may be especially susceptible to external temperature. The temperature inside a mother's womb is 38° C. (100.4° F.). As soon as an infant leaves the warmth of the womb at birth, the infant is exposed to a much colder environment and immediately starts losing heat. Because an infant cannot regulate its body temperature as well as an adult, the infant cools down and heats up much faster than an adult and therefore, is able to tolerate only a limited range of environmental temperatures.
Babies who are born prematurely, with low-birth-weight (LBW), or weak and ill-developed, may have a particularly difficult time regulating body temperature because their nervous regulating mechanisms are often underdeveloped. If heat loss is not prevented and is allowed to continue, such babies will develop hypothermia. A hypothermic baby, especially if it is small, sick, or is of LBW, is at increased risk of developing health problems and of dying.
Twenty million premature and LBW babies susceptible to thermoregulation problems are born every year around the world. In developed countries, LBW babies are placed in incubators to regulate their temperature. Typical incubators are very expensive, costing thousands of US dollars. Such incubators require active electrical connections and may require delicate electronics. They are also heavy and cumbersome. These factors typically limit the use of such incubators to the urban hospitals of well developed countries and prevent typical incubators from being portable.
Unfortunately, eighty percent (80%) of LBW babies are born in rural areas of developing countries where typical incubators either do not exist or are hardly available. In India alone, for example, a third of all babies born are LBW. Three and a half (3.5) million LBW babies die each year, while those who survive often develop life-long health problems like the early onset of diabetes, heart disease and low IQ.
As mentioned above, traditional incubators cost thousands of dollars, and are available primarily only in urban hospitals. Even where available, incubators in developing countries are often in disrepair. Regardless, most rural parents cannot afford to get their babies to these urban hospitals. In summary, many LBW babies effectively have no access to incubators.
To address the limited access to incubators in the rural areas of developing countries, a low cost incubator design to help the needs of LBW babies was proposed by MIT students. MIT students proposed an incubator that included a small dome tent structure suspended over a double layered floor. The floor contained an opening to receive a heating mattress. The heating mattress incorporated a phase change material (PCM) to passively regulate temperature. Although costing far less than incubators used in hospitals, the MIT incubator design has various drawbacks.
For example, in the dome tent structure of the MIT incubator design, the baby can not be held by the parent while in the incubator. If the baby needs comforting or nursing, the baby must be removed from the incubator and risk exposure to temperature change in order to do so. In addition, because the baby is not secured within the dome tent structure and is free to roll around, it is possible, if left unsupervised, for the baby to roll out and lose the environmental protection the dome tent provides. Furthermore, the dome tent structure does not provide any warmth for the child outside of the heat coming from the heating mattress. This makes it an inefficient design and susceptible to rapid cooling if the heating mattress fails. Also, the dome tent structure is not a rugged design suitable for longevity and the harsh environments associated with transport. The rods used in the tent structure could be easily broken or the fabric used on the outside of the tent could be easily torn or crumpled.
In addition to the thermal regulation help an incubator provides, LBW babies often need the immediate medical attention of a doctor. Therefore, the ability to transport the baby while remaining in the incubator is an important factor in a solution for infants born in rural areas. The structure of the MIT dome tent design is not rigid enough to support the weight of the baby during transport. In addition, the dome tent design does not conform closely enough to the shape of the baby to allow the baby and the dome tent structure to be easily carried together. Therefore, attempts to transport the dome tent while the baby is inside could lead to injury.
Infant or baby warming devices that include super-cooled inorganic PCMs have also been proposed. Super-cooling is the cooling of a liquid or saturated solution below its freezing point without crystallization taking place. Super-cooling is possible because of the lack of solid particles around which crystals can form. Crystallization rapidly follows the introduction of a small crystal (seed) or agitation of the super-cooled solution. However, the final temperature attained by the super-cooled solution, and thus the amount of heat released during the exothermic phase change of crystallization, depends on the temperature prior to activation.
The Cooper Surgical Transwarmer heat source, as disclosed in U.S. Reissue Pat. No. 35,586, is an infant warming mattress aimed at temperature regulation. The Transwarmer uses a super-cooled salt solution of sodium acetate (inorganic PCM) that may be activated by a button and that subsequent to activation, releases heat in an exothermic reaction (heat of crystallization). Because of their dependence on the initial temperature, inorganic PCM's that are super-cooled, such as those in the Transwarmer, may not have a predictable and stable final temperature. The unpredictability of temperature is dangerous and may cause burning. In addition, warmers using inorganic PCM's like the Transwarmer, do not maintain their temperature for very long periods of time, i.e., typically only around two hours. Furthermore, devices like the Transwarmer are single use devices making them impractical for use outside of hospitals where they can not be stocked.
In view of the foregoing, a need exists for an improved thermal regulation device and method that addresses or at least ameliorates one or more of the problems associated with existing thermal regulation designs.